I've decided to go with 4 of these on my 300g http://www.alibaba.com/product-gs/546432064/2012_dimmable_led_aquarium_light_with.html
I think being able to dim the reds and greens will help me dial in the color I want and being only a FOWLR I think it will look great.
I think you are mistaken, those colors will be on one of the other dimmer switches, there is not a dimmer for blue, one for white, one for red, and one for green. So while you can control them to a degree, it wont be separate. I think a couple people h ave got these units, maybe someone can chime in.